A 20 N stone is suspended from a wire and its length changes by 1%. If the Young's modulus of the material of the wire is 2 x 10¹¹ N /m², the area of cross-section of the wire is

• A

  ${10}^{-3}{\mathrm{mm}}^2$

• B

  ${10}^{-2}{\mathrm{mm}}^2$

• C

  ${10}^{-1}{\mathrm{mm}}^2$

• D

  1mm²